Where is North?

To find your way using a magnetic compass with a map, you need to know the difference between magnetic north and map north. This difference is called ‘grid magnetic angle’, and in the UK it is derived from a model of the Earth’s magnetic field, which is updated every year. The variation To go north, you just follow your compass towards magnetic north, right? Not quite. Geophysicists have to work hard so we can continue to navigate with map and compass. Susan Macmillan and Tom Shanahan describe how the UK magnetic repeat station network helps. in grid magnetic angle reflects changes in the Earth’s magnetic field arising from sources in the Earth’s fluid outer core. We don’t yet understand these changes well enough to make good forecasts, so we need to monitor them continuously.